Numerous processes and machines exist to create folds in a stream of web material or in cut sheets issuing from a stream of web material. A typical interfolding apparatus has two rotating interfolding rolls that issue a stream of interfolded web material. One packer finger works in cooperation with each roll to create a fold in the material or sheet.
In operation, separate streams of web material are delivered to individual cutting rolls where the web material is cut into sheets. The sheets then move downward to corresponding interfolding rolls that are positioned to form a nip therebetween. The interfolding rolls rotate in opposite directions and receive the newly-cut sheets of web material from the cutting rolls.
The sheets are usually staggered with respect to the first and second interfolding rolls so that a middle portion of a first sheet of one roll passes through the nip at approximately the same time as leading and trailing edges of sheets of the opposite rolls. At this time, vacuum or mechanical grippers of the first roll grab the center of the first sheet and the leading and trailing edges of the opposing sheets to begin a fold in the first sheet and to capture the leading and trailing edges within the fold.
As the gripper rotates close to the packer finger, the force from the gripper decreases and the packer finger pushes the sheet from the interfolding roll to a position where the fold can be pressed with the leading and trailing edges of the opposing sheets being folded therebetween. This process continues alternately with the other interfolding roll to form a stack of material. In many situations, it is desirable to count out a specific number of sheets for packaging purposes. Additional fingers commonly referred to as count fingers and package building fingers can be used to separate a stack with a desired number of sheets. The count fingers are manipulated into the stack of folded web material at a specific point to define a clip having a known quantity of items.
The prior art systems generally employ the use of one packer finger per roll to create a fold in the stream of web material or sheet of web material. The size and shape of the single packer finger per roll varies in the prior art. The profile of the packer finger as well as the length can determine how much indentation or damage is inflicted on the web material, as well as the quality and location of the fold. The amount of surface area and the length of the packer finger that contacts the web material can contribute toward weakening of the web material as well as incorrect folding.
An advantage of packing the web material with a short packer finger is that the packing force exerted by the short packer finger is applied directly adjacent to the gripper portion of the interfolding roll so that very little force will be applied against the portion of the folded sheet that is upstream of the fold (i.e., the upper panel). However, it is difficult for the short packer finger to create enough friction to properly hold the previously folded sheet in place on the stack of interfolded sheets while the opposite interfolding roll is pulling the upstream portion of the sheet to the other side. If the short packer finger applies greater force on the stack of sheets to hold the previously folded sheet, the web material can be disrupted or damaged. In addition, the short packer finger is unable to properly remove air from the sheets coming off of the rotating rolls when they are being folded thereby allowing air entrapment to potentially cause damage to the sheets being folded at high speeds.
An advantage of creating a fold with a longer packer finger is that the long packer finger can create the right amount of friction to hold the previously folded sheet on the stack of interfolded sheets when the upper portion of the sheet is being tugged down by the opposing interfolding roll to form a fold. Compared to the shorter packer finger, the longer and flatter packer finger generates a larger area of friction force with the same or less force on the stack of sheets. The disadvantage to using the long packer finger is that the long packer finger pushes the sheet of web material at a location that is higher up on the rotating roll when creating a fold. This can cause the sheet of web material to stretch, tear, or become more porous. A longer packer finger provides less control over where the sheet of web material releases from the roll and therefore affects the location of the fold. Also, the longer packer finger transmits more force to the leading edge of the opposing sheet and may cause the leading edge to prematurely release from the gripper on the opposite roll.
In light of the above design limitations, a need exists for a packer finger apparatus that can overcome the limitations of the prior art. A need exists for an interfolding apparatus that has packer fingers that can quickly and precisely fold and pack a stream of web material without causing damage to the sheets. Some embodiments of the invention achieve one or more of these results.